gofar99 Messages: 1949 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi, A lot of thought went into the project . I have been working for about 8 months or so on a RIAA preamp. I tried several variations and none have quite done what I want. I have no problem with gain, overload, Z out, frequency response. The one area I want is a S/N of over 90 dbv at 1 volt output. I can get 85 now. The best topology so far is a 12AX7 SRPP feeding a second 12AX7 SRPP followed by a E88CC cathode follower. The equalization is active between the third and first stage. The active mode gave better S/N than a passive one between the first and second stages. I sympathize with the problems you have experienced with measurements. I have a raft of test gear incl 2 DSO, a HP distortion analyzer, two signal generators and more meters than I can count. Still the process of measuring RIAA preamps is both tedious and can be misleading. When I get it a little closer to what I want, I'll post it.
Where did you get the power transformer? Small ones for this type of project are difficult to locate except through overseas sources.
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. I have been working for about 8 months or so on a RIAA preamp. I tried several variations and none have quite done what I want. I have no problem with gain, overload, Z out, frequency response. The one area I want is a S/N of over 90 dbv at 1 volt output. I can get 85 now. The best topology so far is a 12AX7 SRPP feeding a second 12AX7 SRPP followed by a E88CC cathode follower. The equalization is active between the third and first stage. The active mode gave better S/N than a passive one between the first and second stages. I sympathize with the problems you have experienced with measurements. I have a raft of test gear incl 2 DSO, a HP distortion analyzer, two signal generators and more meters than I can count. Still the process of measuring RIAA preamps is both tedious and can be misleading. When I get it a little closer to what I want, I'll post it. 
